Evaluation of three methods for the measurement of urea nitrogen in serum as used on six instruments

The authors compared three urea nitrogen methods using six instruments: (1) the diacetyl monoxime method used with a continuous flow analyzer Sequential Multiple Analyzer Model 4 + 2; (2) the diacetyl monoxime method used with an older continuous flow analyzer (Sequential Multiple Analyzer Model 6/60; (3) the diacetyl monoxime method used with a third continuous flow system, AutoAnalyzer Model I; (4) the urease-conductivity method performed on the Beckman System I; (5) the urease-glutamate dehydrogenase method performed on the DuPont Automatic Clinical Analyzer; (6) the urease-glutamate dehydrogenase method done on a centrifugal analyzer, CentrifiChem. We evaluated each method for the following: (1) within-run precision; (2) between-day precision; (3) linearity of the relationship between concentration and instrument output; (4) specificity; (5) carry-over; (6) comparison of urea nitrogen values for samples from patients.